Leg Problems in Poultry

Leg health is an integral part of the economics of poultry. It is estimated that approximately 12.5 billion poultry worldwide suffer from various leg injuries each year (Nicol, 2013; Xu et al.,2025). According to a review of Huang et al (2023), leg diseases in the United States have caused economic losses of more than 80 million to 120 million US dollars in the broiler industry (Huang et al. 2023). These could indirectly lead to a further decline in reprocessing margins and reduce the gross profit of the poultry industry by 10% to 40% (Paz 2010).

Many broilers are reared using modern intensive production systems for their lifetime within high density housing and reared from hatch to slaughter weight within approximately 40 days. Legs problems limit the normal movement and feeding ability of broilers and the abnormal skeletal growth and development inhibits broiler growth and weight gain rates. Legs issues in addition to negatively impacting bird performance, it also negatively affects meat and bone quality (Huang et al. 2023; Xu et al.,2025), viability and welfare (Edwards et al., 1984, Burton et al., 1981 and Riddell et al., 1985). Chickens with leg diseases include joint cysts, leg weakness, and bone deformation (Cao et al. 2020; Huang et al. 2021) and animal welfare because birds feel pain and cannot reach feed and water (Bradshaw et al., 2002). Poor leg health and lameness can occur from multiple origins (Gentle, 2011).

a) Tibial dyschondroplasia (TD) is a nutritional metabolic disease. TD is of economic importance to the poultry industry. Increases in mortality, culling, downgrading of carcasses, and trimming of deformed legs at processing have been attributed to TD (Burton 1981; Riddell, 1985). It occurs due to apoptosis and vascularization of chondrocytes in the broiler tibia, resulting in a build-up of dead chondrocytes (Huang et al. 2017; Huang et al. 2019; Huang et al. 2019; Jahejo et al. 2022). It is known to be a common disease in fast-growing broilers and one of the leading causes of lameness in broilers (Huang et al. 2018; Huang et al. 2019a). The disease is characterized by impaired walking function, reduced growth rate, and tibia deformation. In the early stages, most cases do not exhibit obvious symptoms (Jahejo et al. 2022). in the later stages, symptoms include ataxia, reluctance to walk, staggering, changes in posture, and leg bone deformities (Huang et al. 2018; Cao et al. 2020). Severe cases of TD can lead to leg splitting, making it difficult for broilers to walk without assistance from their wings (Xu et al., 2022).

b) Femoral head necrosis is a common leg disease in broilers, occurring at an incidence rate of 30% to 40%. It typically affects broilers between the ages of 5 to 6 weeks (Fan et al., 2021). Abnormal walking may appear in the later stages of the disease (Maus et al. 2018). Affected chickens exhibit a trembling gait and walk with minimal support from their wings, often in an inward arc style (Zhang et al. 2017). Only one leg is affected in sick broilers, which are bent outwards and backward, or to one side. In cases where both legs are affected simultaneously, the affected broilers often have a belly-recumbent position (Maus et al. 2018). Additionally, deceased broilers may have a distinctive posture, with their legs flattened back and their heads on one side (Liu et al. 2021).

c) Gout in chickens is a nutrient metabolic disease of broiler chickens, caused primarily by the overproduction or under-excretion of uric acid. This leads to high levels of uric acid in the blood, resulting in hyperuricemia (Dalbeth et al. 2021). The excess uric acid is then deposited in various areas, such as the joint capsule, joint cartilage, the areas surrounding the joints, the thoracic, and abdominal cavities, and the surfaces of different organs (Liu et al. 2023). There are two main categories of gout in broilers, which are based on the causative factors and the clinical manifestations of visceral gout and joint gout (Liu et al. 2022). Arthritic gout has a lower incidence compared to visceral gout and tends to be more chronic. The clinical symptoms include urate deposits in the joints of the wings, legs and feet, causing swelling and pain in the tarsal joints (Hong et al. 2020). Broilers affected by this type of gout often assume a standing or crouching position on one foot and have trouble in walking. Visceral gout is usually more prominent during the night and is associated with a decline in egg production or even a complete cessation of egg laying. Additionally, it often leads to the production of sandy and smaller-sized eggs (Li et al. 2022)

d) Bacterial chondronecrosis with osteomyelitis (BCO) is considered one of the most common skeletal diseases causing lameness in broilers (Wideman 2016). There are two main types of disease. The first is infectious, caused by bacteria like Escherichia coli, salmonella, and staphylococcus (Namee et al. 2000). The second type is non-infectious, primarily caused by vitamin deficiencies, poor digestion and improper feeding management (e.g. improper feed ratios, uncomfortable temperatures, and cloudy air) during broiler production (Wideman 2016). Broilers with BCO are vulnerable to bacterial infiltration and subsequent hematogenous colonization in the proximal femoral and tibial growth plate, resulting in necrosis and eventually lameness (Wideman 2016; Wijesurendra et al. 2017). When the injury occurs at the end of the proximal femur, the broilers often use one or both wing tips to support their body or flex the hip joint while moving (Ramser et al. 2022).

Birds with BCO succumb to bacterial infiltration and subsequent hematogenous colonization of the proximal femoral and tibio-tarsal (tibial) growth plates; this leading to necrosis and eventually lameness (Wideman, 2016; Wijesurendra et al., 2017).

e) Infectious synovitiss is a systemic disease in broilers caused by an infection with Mycoplasma synoviae (Chen et al. 2022). It often affects broilers sub clinically (showing no obvious signs of illness), until a stressful event occurs, which triggers the infection systemically and influence the synovial membrane of the joints and tendons (Sun et al. 2017). Breast abscesses are a common occurrence in affected broilers of any age. In affected broilers, the tarsal joints, toe joints or toe heels become swollen and deformed. Affected broilers may exhibit increased skin temperature and fluctuation when touching the swollen part of the leg (Feberwee et al. 2022). Limping is a common symptom in most sick broilers. Then joint swelling becomes more prominent, making it challenging for broilers to stand and move, and in severe cases, it can lead to death (Yadav et al. 2022)

f) Avian osteopetrosis is an infectious bone proliferation disease caused by a replication-competent avian leukaemia sarcoma group virus (Fothergill 2017). The disease is more serious in high-yielding hens and caged laying hens and is also known as caged-layer fatigue (CLF). The causes of its susceptibility mainly include environmental and nutritional factors, such as insufficient or unbalanced calcium and phosphorus in feed (Regmi et al. 2016; Lin et al. 2017; Yang et al. 2020). Some common symptoms of avian osteopetrosis include a “boot-like” swelling of the metatarsal bones on both sides, slight forward bending, and increased local temperature in active lesions. By palpating the tibia and ulna, diaphyseal thickening can be detected (Nishiura et al. 2020). The higher the productivity of the chicken, the higher the mortality rate. When the disease progresses to a chronic stage, the onset in laying hens is usually characterized by landing on the hocks, inability to stand and lying on the bottom of the cage (Teng et al. 2020). Fractures occur in chickens with severe disease (El-Saadony et al. 2022). Furthermore, affected cockerels lose their ability to crow and engage in sexual activities.

g) Viral arthritis is caused by avian reovirus (ARV); it is characterized by arthritis and tenosynovitis of the gastrocnemius tendons (Palomino-Tapia et al. 2018). affected broilers usually exhibit abnormal ambulation, including lameness and swaying. Abnormalities are observed only in the feet, but they gradually spread to the knees as the disease progresses. The tarsal joint, in particular, is prone to swelling of varying degrees, and the legs become stiff and unable to stretch normally (Sellers., 2017). Affected broilers tend to sit on their joints, and when artificially driven, they use their toe joints to support and jump forward while their palms off the ground. In the middle stages of the disease, broilers experience severe lameness and splay legs due to inflammation and rupture of the hock. As the condition progresses, affected chickens also exhibit a significantly decreased appetite, severe diarrhea, and the excreted feces have a distinct fishy smell (Goldenberg., 2022).

Prevention and treatments of Leg diseases in poultry

Since leg disease is a multi-causative disease, it may be prevented or controlled by genetics, nutritional factors, feeding and management methods, intercurrent infections, and mycotoxin ingestion, seasonally, stocking density, feed form (Kierończyk 2017).

Genetic and growth rate

Genotypes influence many traits associated with leg health. With genetic improvement and Intensive farming and the continuous improvement of management techniques, broiler chickens are growing rapidly. In fast growing male birds, the incidence of TD can be as high as 30 to 49% (Leeson et al., 1995). Heavier birds are more likely to develop more TD because the proximal tibiotarsus shows the fastest growth plate development in fast-growing birds [Riddell,1975). Excessive muscle growth in broilers compared to the rate of bone growth results in inadequate leg bones supporting their body weight, leading to increased fractures and infectious diseases (Guo et al. 2019; Huang et al. 30 2019; Harash et al. 2020; Pritchard et al. 2020). There is evidence that in optimizing traits for production the resulting birds, whilst producing meat at a low cost, have a reduced viability and welfare with poor walking ability, or locomotion, a primary concern. A way to reduce leg problems via genetics is choosing a slow growth breed such as Sasso, LaBelle Patrimoine, etc.

Nutritional Factors

It has been shown that dietary electrolyte imbalance and particularly high levels of chloride seem to be major factors in many field outbreaks of TD (Riddell, 1975). It has also been shown that TD incidence and severity are high in birds fed diets containing low calcium in combination with moderate levels of phosphorus (Edwards, 1984).

Management

Management factors, including provision of perches, have been explored to improve the health and welfare of the domestic fowl. It is possible that exercise in the form of perching may also reduce the impact of leg problems.

Placing barriers or ramps within the pen caused an increase in the mass and dimensions of broiler breast and leg muscles, indicating that exercise could be encouraged by altering pen design and that such additions to the pen can improve the overall physical condition of the birds. The incidence of TD was lowest (6.1%) among birds with access to horizontal perches.

The percentage of mean bone ash can serve as a general measure of bone mineralization. It appeared that males that are given access to horizontal perches at a density of 15 birds/m2 have the highest degree of bone mineralization as measured by percentage bone ash

Previous research has highlighted associations between management practices and levels of leg disorders. Most attentions have focused on the partially effective practices of reducing feed quantity or the nutrient density of feed or providing more than 1-hour of darkness each 24-hour period.

Seasonality has been noted to impact leg health; for example, higher percentage of leg abnormalities have been reported in the summer.

Stocking Density: There has been debate about the importance of stocking density as an influence on bird welfare and locomotion. Within limits, putting as many birds in a house as possible for each rearing cycle will improve profitability. For every 1 kg/m² increase in stocking density as measured at the time of the flock assessment, there is a 0.013 deterioration in flock gait score. Percentage bone ash tended to decrease with increasing stocking density.

The detrimental effect of higher stocking densities may be more complex, reflecting not only a lack of room available for birds to move and exercise, but also the extra environmental loading from increased biomass (e.g. additional ammonia and litter moisture). A new Directive was approved in 2010 to prevent farms from stocking birds at densities over 39 kg/m2 in flocks with previous mortality levels.

increasing stocking density has been shown to decrease body weight and increase feed conversion and reduce activity level. Reduced activity has also been implicated as a factor involved in the development of leg problems in broiler chickens.

Prevention and control

TD can be prevented by reducing growth rate through light or feed restriction and diet modification (Lilburn, 1989 and Edwards, 1987). Antibiotics are routinely used during different stages of broiler rearing and their use can be quite difficult to quantify accurately.